Vehicle navigation system

ABSTRACT

In a vehicle navigation system, when a voice control part, which is displayed on a screen, is switched off, a voice control part inhibits voice guidance from being output to a speaker. Now, if a current-location/guide selection key is operated, the voice control part creates voice guidance according to the operation of the selection key and outputs the voice guidance from the speaker. With this navigation system, aural route guidance is possible only at the driver&#39;s request.

This is a continuation of application Ser. No. 08/95,440, filed Jul. 23,1993 now U.S. Pat. No. 5,343,399.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a vehicle navigation system for aurallydirecting the movement of a vehicle so that it will reach its intendeddestination.

2. Description of the Related Art

Various kinds of apparatuses have been developed for use on vehicles inan effort to reduce the driver's burden; among such conventionalapparatuses, there is a navigation system for directing the movement ofa vehicle so that it will reach its intended destination. Theconventional navigation system is equipped with the function of showingthe driver a route to be selected when the vehicle passes a turningpoint such as a crossing and the function of directing the routeaurally. This conventional navigation system is exemplified by JapanesePatent Laid-Open Publication No. HEI 1-173819.

With the conventional navigation system using aural guidance, notice asto whether a vehicle should turn to the right or left is automaticallygiven to the driver aurally when the vehicle arrives at a crossing, asthe current position of the running vehicle is detected at all times.For instance, aural guidance such as "turn to the left at the crossing100 m ahead" is given when the vehicle arrives at a position 100 m shortof the crossing.

Therefore, even in the absence of local map knowledge, the driver cantake a correct driving route, without watching the display of thesystem.

Assuming that the vehicle is traveling on a road the driver knowssomewhat, an aural notice would not be necessary. Instead, the routewill have been searched as a matter of precaution. Any display on thescreen will not disturb the driver if he/she does not look at thescreen, but an aural notice will reach the driver's ears whether theylike it or not. As a hypothetical solution, such an aural notice couldbe cut off by means of a switch so that no announcement disturbs thedriver.

If route searching is being made when traveling, it may be that thedriver requires some help with the navigation. Practically speaking,route guidance on the display screen is more difficult to follow, ascompared to aural route guidance. It is therefore preferable that thedriver enjoy aural route guidance only at the driver's request.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a vehiclenavigation system which can give timely voice guidance at the driver'srequest.

According to this invention, there is provided a vehicle navigationsystem comprising: map information storage means; route computing meansfor searching for a route to an intended destination of the vehicleusing the map information stored in the map information storage means;route guide and control means for displaying the computed route on adisplay screen and for outputting voice guidance via a speaker; on-offselecting means for selecting whether or not the voice guidance shouldbe output; inhibition means for inhibiting outputting of the voiceguidance if the on-off selecting means selects that the voice guidanceshould not be output; input means for inputting a request for outputtingthe voice guidance; voice guidance creating means for creating the voiceguidance in response to the output request from the input means; andvoice guidance voice output means for releasing the inhibition status ofthe inhibition means for a predetermined period of time to output thevoice guidance created by the voice guidance creating means.

With this arrangement, if the driver makes a request while voiceguidance is inhibited (usually, route guidance is displayed on thescreen), it is possible to output voice guidance. Therefore, the driverwill not be disturbed by any voice guidance unless he/she makes arequest; that is, the driver can uninhibit voice guidance if he/shewishes to hear such voice guidance. Thus it is possible to give suitablevoice guidance to meet the driver's request.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a vehicle navigation system accordingto a first embodiment of this invention;

FIG. 2 is a diagram showing an example of displayed route guidance;

FIG. 3 is a diagram showing another example of displayed route guidancearound a crossing;

FIG. 4 is a block diagram showing the manner in which voice guidance isoutput from a voice control unit of the system;

FIG. 5A is a diagram showing a voice control display on the menu screen;

FIG. 5B is a diagram showing another voice control display on the menuscreen;

FIG. 6 is a flow diagram showing h process of navigation when a requestfor voice guidance is made;

FIG. 7 is a flow diagram showing another process of navigation when arequest for voice guidance is made;

FIG. 8 is a block diagram showing a modified navigation system accordingto a second embodiment of the invention;

FIG. 9 is a flow diagram showing the navigation process of the secondembodiment;

FIG. 10 is a block diagram showing another modified navigation systemaccording to a third embodiment of the invention;

FIG. 11 is a diagram showing the operation of the system of the thirdembodiment when the vehicle is going to turn to the right at a crossing;

FIG. 12 is a block diagram showing still another modified navigationsystem according to a fourth embodiment of the invention;

FIG. 13 is a diagram showing the operation of the fourth embodiment whena measurement error of the current position of the vehicle is made; and

FIG. 14 is a diagram showing the operation of the fourth embodiment whena previous notice and a final notice are made when the vehicleapproaches a crossing.

DETAILED DESCRIPTION

Preferred embodiments of this invention will now be described withreference to the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing a vehicle navigation system accordingto a first embodiment of this invention. The navigation system includesa map information storage unit 10 in which map information, such as roadnames, place names (crossing names), building names and river names, isstored and from which the stored map information may be read asrequired. The navigation system also includes a GPS receiver 14utilizing the global positioning system (hereinafter called "GPS") formeasuring the current position of a vehicle, a direction sensor 16 fordetecting the direction of movement of the vehicle based on the earth'smagnetism, and a distance sensor 17 for detecting the distance coveredin terms of r.p.m. of the wheels. Based on the results of detection ofthese sensors, a current position measuring unit 12 locates the currentposition of the vehicle. Information from a steering sensor 19 isutilized such as in map matching to compensate the current position ofthe vehicle to the position of a crossing on a map when the vehicleturns to the right or left at the crossing.

For guiding the vehicle to its intended destination, the destination isindicated on the screen of a display unit described below and is inputby place name, and the route from the current position, which iscomputed by the current position measuring unit 12, to the destination,is computed by a route computing unit 22 having an arithmetic controlunit 20, whereupon the computed route is stored in a route storage unit24. In this route computing, any suitable route searching method may beused.

A destination is input and then a route is decided, whereupon actualroute guidance takes place. A route guiding unit 26 of the arithmeticcontrol unit 20 reads map information around the vehicle from the mapinformation storage unit 10 and indicates this on a display unit 28,superposed with the current position and direction of movement of thevehicle as well as the route stored in the route storage unit 24.

The display unit 28 is mounted in an instrument panel near the driver'sseat so that the driver can confirm the current position of the vehicleby watching the display unit 28 and can obtain information about afuture route. One example of such a display is shown in FIG. 2. In FIG.2, the selected route is indicated by a thick solid line 100 and theremaining roads are indicated by thin solid lines 102. The currentposition of the vehicle is indicated by a circle 104, and the directionof movement is indicated by an arrow 106. Roads may be indicated byeither solid lines of different thicknesses or different colors.

When the vehicle approaches a crossing 108, where the vehicle has tomake a turn, the display on the screen is switched to that of FIG. 3,and the crossing name 110 and the distance 112 to the crossing aredisplayed on the screen. The route guiding unit 26 instructs a voicecontrol unit 30 in the form of an amplifier to generate a voicecorresponding to the route guidance at the crossing simultaneously withthis change of display. The voice control unit 30 reads from a voicestorage unit 32 information stored therein as digital data, and thedigital data is converted into analog signals to activate a speaker 34.A route direction, for example, "Turn to the left at * * * crossingabout 300 m ahead." is issued to the driver from the speaker 34 toperform the route guidance. This voice direction is given for everypredetermined distance until the vehicle has passed the crossing.Assuming that the vehicle is traveling on a road having two or morelanes, a first aural notice is given at a position 700 m short of thecrossing, a second notice is given at a position 300 m short of thecrossing, a final notice at a position 100 m short of the crossing.These guidance voices are stored in the voice storage unit 32 in termsof digital data for every phrase. For outputting voice guidance, severalphrases are read from the storage unit 32 to create a composite guidancesignal to be output from the speaker 34. The timing to output voiceguidance is detected by the route guiding unit 26, and the voice controlunit 30 processes the voice output.

In this embodiment, the screen of the display unit 28 is constituted bya touch-sensitive panel serving as an input unit 18. The driver caninput data by touching the place name indicated on the display unit 28.The input unit 18 includes a menu key 18a for going back to a menuscreen to select a process such as inputting the destination orcontrolling the voice, a current-position/guide key 18c for going backto a current-position indicating screen or requesting route guidance, anair-conditioner key 18d for displaying an air-conditioner controlscreen, an audio key 18e for displaying an audio control screen etc.

Further, a voice notice is output using the speaker 34 of an audio set.Specifically, out of four speakers of the audio set, one speaker (i.e.,a speaker 34a near the driver's seat) is used to output voice guidance.For this purpose, the speaker 34a near the driver's seat is connected tothe audio set 40 via the voice control unit 30, and the output of theaudio set 40 is connected to the remaining three speakers 34. When it isnot necessary to output any voice guidance, the voice control unit 30supplies the output from the audio set 40 to the speaker 34a. When it isnecessary to output voice guidance, the voice control unit 30 supplies avoice guidance signal, instead of the output from the audio set 40, tothe speaker 34a. As a result, the output of the audio set 40 isprohibited, and the voice guidance is output from the speaker 34a. Thethree speakers 34 other than the speaker 34a are not influenced by thevoice guidance output.

FIG. 4 shows the manner in which voice guidance is output from the voicecontrol unit 30. Digital voice data read from the voice storage unit 32is stored in a RAM (not shown) and is processed such as by phrasecomposition, whereupon the resulting data is supplied to adigital-analog converter 30a where it is converted into an analog voicesignal. The analog voice signal is then amplified, by an amplifier 30b,to a predetermined value specified by a volume signal and is supplied toa switch 30c.

The switch 30c supplies an audio signal or voice guidance from the voicecontrol unit 30, one at a time, to the speaker 34a. Normally, the switch30c supplies an audio signal to the speaker 34a. Only when voiceguidance is to be output, the switch 30c selects the signal from theamplifier 30b. This switching is made by the voice control unit 30,based on the signal from the route guiding unit 26.

Volume control of the voice guidance is determined by touching a volumecontrol indication on the menu screen of the display unit 28. The menuscreen of the display unit 28 is exemplified by those of FIGS. 5A and5B. The voice control indication is seen at the bottom of the menuscreen. When the indication "OFF" is touched, the attenuation factor ofthe volume signal will be 128 dB to stop voice guidance. If the "OFF"key is touched on this screen, the voice control unit 30 holds theswitch 30c connected to the audio set so that the switch 30c is notoperated even when it receives a switching control signal at the timingof guidance output from the route guiding unit 26, thus stopping anyvoice guidance output.

Now, if the current-position/guide key 18c is touched, the screen ischanged to the route guiding screens of FIGS. 2 and 3 so that routeguidance takes place by the screen. However, since the voice guidance isprohibited as the switch is held, no guidance will be output. Duringthis voiceless route guiding, if the current-position/guide key 18c istouched, it will be regarded as a request for voice guidance. Inresponse to this request, the voice guidance will be output. Thisoperation will now be described in connection with FIG. 6.

It is determined whether the voice volume is set to be off (S11). If thevoice volume is off, it is determined whether or not a request for voiceguidance has been made, namely, whether the current-position/guide keyon the menu screen has been touched (S12). If the current-position/guidekey has not been touched, there is no request for voice guidance and sothe process for outputting voice guidance will not be made.

At S11, if the voice volume is not off (i.e., if the normal voiceguidance is to be made) and if a request for voice guidance has beenmade, it is confirmed whether or not the voice guidance is necessary(S13). In other words, if route guidance has not originally been madeand if only the current position of the vehicle is displayed, then theprocess for outputting voice guidance will not be made.

If the voice guiding process is to be made during route searching, voiceguidance phrases are composed. Namely, phrases stored in the voicestorage unit 30 are combined to create a voice guidance signal. Thenormal voice guidance takes place when the vehicle reaches apredetermined position 300 m short of a crossing where the vehicle is tomake a turn. But this guidance should take place at a timing differentfrom the timing of the normal voice guidance. Specifically, guidancewill take place when the driver has touched the current-position/guidekey. The contents of the guidance depends on the situation. For example,if the vehicle reaches a position 500 m short of the crossing where thevehicle is to make a turn, the notice "Turn to the left at * * *crossing about 500 m ahead." is given. If the vehicle is traveling neara crossing where the vehicle is to pass, a notice such as "Passingnear * * * crossing." is given. Thus phrases will be composed to createan appropriate notice.

Then the voice control 30 sends an activation signal to a mute circuit40a of the audio set 40 to mute the output of the audio set 40 (S15).Then the switch 30a is operated to select the voice guidance (S16), andvoice guidance is output from the speaker 32a (S17). Then the switch 30ais further operated to select connection to the audio set 40 (S18) sothat the muting of the audio set 40 will be released (S19) to finalizethe navigation process.

According to this embodiment, if the current-position/guide key 18c istouched while voice guidance is inhibited, it will be regarded as avoice guidance request having been made at the current position of thevehicle, whereupon voice guidance will be output. Therefore, thisnavigation system is particularly useful when the driver is to be guidedonly when required while traveling along a road the driver knows fairlywell.

FIG. 7 shows another navigation process, which is basically identicalwith that of FIG. 6. In this example, it is first determined whether ornot a voice notice is necessary (S21). If the voice notice is necessary,phrases are composed (S22). For route guidance, voice notices arepreviously created to correspond to the various possible routes of thevehicle. Then it is determined whether or not the voice volume is off(S23). If the voice volume is off, it is determined whether or not arequest for voice guidance has been made (S24). If the voice volume isnot off and a voice guidance request has been made, a voice notice willbe output. The process for voice guidance output S25-S29 is identicalwith that of S15-S19.

By touching the indication "LOW" on the menu screen, it is possible toincrease the amount of attenuation of the amplifier 30b by apredetermined increment at every touch. Conversely, by touching theindication "HIGH" on the menu screen, it is then possible to reduce theamount of attenuation of the amplifier 30b by a predetermined decrementat every touch.

If the menu key 18a is depressed, it is possible to display the menuscreen immediately so that voice guidance may be inhibited.

Second Embodiment

FIG. 8 shows a modified navigation system according to a secondembodiment. In this embodiment, an off-route discriminator 26a ismounted in the route guiding unit 26. When the driver stops at a fuelstation or a shop alongside the road, the current position of thevehicle will necessarily be off a scheduled route. Then the off-routediscriminator 26a of the route guiding unit 26 recognizes that thecurrent position of the vehicle is off the route as the result ofcomparison therebetween. In such an event, a control signal will besupplied to the voice control unit 30 to stop unnecessary voiceguidance.

FIG. 9 is a flow diagram showing the operation of the route guiding unit26 and the voice control unit 30. First of all, it is determined whetheror not the current position of the vehicle is on a scheduled route(S101). This discrimination is made by the off-route discriminator 26awhich compares the current position of the vehicle with the scheduledroute. If the vehicle is on the route, it is determined whether or notvoice guidance is necessary (S102). If voice guiding is necessary, thevoice control unit 30 is instructed to perform the above-described voiceguiding process (S103).

If the current position of the vehicle is not on the route and hence offthe route, iris discriminated whether or not the vehicle has moved froman on-route position to an off-route position (S104). Thisdiscrimination is made by detecting the value of a flag which is raiseddepending on the result of the above-mentioned discrimination. If theoff-route state has been detected, it is discriminated whether or notvoice guidance is being output (S105). If unnecessary voice guidance isbeing output, the voice control unit 30 is instructed to stop voiceguidance (S106).

In this embodiment, it is discriminated whether or not the vehicle hasmoved off the route. When the off-route state has been detected, voiceguidance will be stopped as it is not necessary. Also when the driverhas moved the vehicle voluntarily to an off-route position, nounnecessary voice will be output from the speaker so that the driverwill not be disturbed by such unnecessary utterances and can enjoycomfortable travelling.

Third Embodiment

FIG. 10 shows another modified navigation system according to a thirdembodiment. In this embodiment, an advance notifier 26b, an advancenotice termination discriminator 26c, a guide inhibitor 26d and a guide26e are mounted in the route guiding unit 26. In FIG. 11, when thevehicle reaches a position (point A) 300 m short of the crossing wherethe vehicle is to turn to the right, an advance notice will beinstructed by the advance notifier 26a of the route guiding unit 26. Inresponse to this instruction, the display unit 28 and the voice controlunit 30 make a display and issue voice guidance, respectively,corresponding to the advance notice. For the voice guidance, a notice"Turn to the right at the crossing 300 m ahead." is given. Hearing thisadvance notice, the driver moves the vehicle to the center line toprepare for turning to the right. Then when the vehicle reaches aposition (B point) immediately short of the crossing, a guide noticewill be instructed by the guide 26d of the route guiding unit 26 and, atthe same time, the display unit 28 and the voice control unit 30 willissue the guide notice in response to the instruction. For the voiceguidance, a notice "Watch out! Turn to the right soon at the crossing."is given. Then the driver makes a right turn following this notice.

In this navigation system, apart from a succession of guidance noticesin which route guidance takes place after an advance notice, it will becontrolled so as to inhibit an aural guide notice at a positionimmediately short of the crossing if no advance notice has been given.For example, if the vehicle stops at a point C in FIG. 11 to make aroute search and then restarts, the above-described guide notice willnormally be given when the vehicle reaches a position immediately shortof the crossing; in this embodiment, this aural route notice will beinhibited. In such an event, even if the driver has received the noticefor right turn suddenly at a position immediately'short of the crossing,it is too late to move the vehicle to the center line and, as a result,it would be difficult to make a right turn. At that time, the drivermight feel as if he/she received an unsuitable notice.

For the foregoing reasons, aural route guidance is inhibited in thissituation. The advance notice termination discriminator 26cdiscriminates whether or not an advance notice has been made by theadvance notifier 26b. In the absence of any advance notice, the guideinhibitor 26d instructs the guide 26e so as to inhibit the aural routeguidance. In response to this instruction for inhibition, the auralroute guidance at a position immediately short of the crossing will beinhibited if no advance notice has been given. Consequently, in suchevent, the driver drives the vehicle according to the instruction on thedisplay unit 28. Route guidance on the display may also be inhibited.

As described above, in the absence of an advance notice, by inhibitingthe route guidance at a position immediately short of the crossing, itis possible to prevent the driver from being disturbed by an unsuitablenotice.

Fourth Embodiment

FIG. 12 shows still another modified navigation system according to afourth embodiment, in which a accuracy detector 36 is mounted in thearithmetic control unit 20. In this navigation system, the accuracydetector 36 detects the degree of measurement accuracy of the currentposition of the vehicle, based on the road information stored in the mapinformation storage unit 10 and the route storage unit 24. When thevehicle is off the road, the accuracy detector 36 judges the vehicle asactually traveling along the road and corrects the current position onthe road, whereupon the difference between the actual current positionand the measured current position will be defined as an error in thecurrent position. For example, if the travelling locus 122 of thevehicle 14 has deviated from the road information 120 stored in, forexample, the map information storage unit 10 and so the vehicle has beenmeasured as traveling at a place where no road exists, this deviation(δ) will be detected as an error of the current position. By observingthis detected error all times, the accuracy detector 36 detects thecurrent degree of accuracy.

Based on the result of detection of measurement accuracy, it will bedecided whether a final notice at a position immediately short of thecrossing should be inhibited or whether the contents of the noticeshould be changed. In this illustrated example, an advance notice isgiven at a position 300 m short of the crossing, and a final notice isgiven at a position 100 m short of the crossing. The degree ofmeasurement accuracy of the current position of the vehicle will be lessthan 300 m in one case and will be at least 300 m in the other case.

If the degree of measurement accuracy is less than 300 m, an advancenotice will be instructed by a advance notifier 26b of the route guidingunit 26 when the vehicle reaches at a position (point A in FIG. 14) 300m short of the crossing where the vehicle is to turn to the right. Uponreceipt of this instruction, the display unit 28 and the voice controlunit 30 perform displaying and voice guidance. For the voice guidance, anotice such as "Turn to the right at the crossing 300 m ahead." will begiven. Hearing this advance notice, the driver moves the vehicle to thecenter line to prepare for making a right turn. When the vehicle arrivesat a position (point B) immediately, e.g. 100 m, short of the crossing,route guidance will be instructed by a final guide 26c of the routeguiding unit 26. In response to this instruction, the display unit 28and the voice control unit 30 issue a display and an aural notice,respectively, corresponding to the route guiding. For the voiceguidance, a notice such as "Watch out! Turn to the right soon at thecoming crossing." is issued by the voice control unit 30. The driverthen drives the vehicle to make a right turn, following this notice.

If the degree of measurement accuracy is at least 300 m, an inhibitor26d will detect it and will issue to the final guide 26c an instructionfor inhibiting route guidance. Therefore, after an advance notice hasbeen given, no voice guidance will take place.

Situations may be divided into three cases in terms of degree ofaccuracy, e.g. less than 50 m, at least 150 m and less than 300 m, andat least 300 m. In the case of less than 150 m, the control for a finalnotice will be carried out after an advance notice. In the case of atleast 300 m, like the foregoing case where the guide notice isinhibited, a final notice will not been given after an advance notice.In the case of at least 150 m and less than 300 m, a final notice willbe issued, but it will be simply "Watch out! Turn to the left." withoutsaying, "soon". Thus if the measurement degree of accuracy is notadequately high, it might be actually much too far to the crossing, inwhich event if the notice said "soon", the driver would have beenmisguided.

What is claimed is:
 1. A navigation system for a vehicle for guiding avehicle along a route to a destination by issuing guidance with a voicesound at an intersection or junction, said navigation systemcomprising:map information storing means for storing map information;computing means for computing a route to a destination by using said mapinformation stored in said map information storing means; presentposition detecting means for detecting a present position of saidvehicle; means for storing said route computed by said computing means;and a route guiding control unit for providing output means with voiceguidance on a basis of said route stored in said means for storing saidroute and said present position of said vehicle detected by said presentposition detecting means, said route guiding control unit inhibitingsaid voice guidance when detecting a predetermined condition, saidpredetermined condition being one of an off-route condition, and adetection that no advance voice guidance related to said voice guidancehas been given.
 2. A navigating system according to claim 1, whereinsaid route guiding control unit compares said present position of saidvehicle detected by said present position detecting means with saidroute provided by said route computing means, and terminates said voiceguidance when detecting an off-route condition based on a result of saidcomparison.
 3. A navigation system according to claim 1, wherein saidvoice guidance relates information regarding a direction said vehicleshould follow at said intersection or junction.
 4. A navigation systemaccording to claim 1, wherein said route guiding control unit is furtherfor:providing pre-information voice guidance when said vehicle reaches apredetermined distance short of said intersection or junction; issuing afinal voice guidance when said vehicle is at a position immediatelybefore said intersection or junction; and inhibiting output of saidfinal voice guidance when said predetermined condition is detected.
 5. Anavigation system for a vehicle for guiding a vehicle along a route to adestination by issuing guidance with a voice sound at an intersection orjunction, said navigation system comprising:map information storingmeans for storing map information; computing means for computing a routeto a destination by using said map information stored in said mapinformation storing means; present position detecting means fordetecting a present position of said vehicle; means for storing saidroute computed by said computing means; and a route guiding control unitfor providing output means with voice guidance on a basis of said routestored in said means for storing said route and said present position ofsaid vehicle detected by said present position detecting means, saidroute guiding control unit inhibiting said voice guidance when detectinga predetermined condition, said route guiding control unitcomprising:informing means for informing pre-information of a correctway which said vehicle should take at said intersection or junction by avoice sound based on said computed route provided by said routecomputing means when said vehicle reaches a predetermined distance shortof said intersection or junction; guide means for providing guidance bysaid voice sound at a position a predetermined distance immediatelybefore said intersection or junction as to which direction said vehicleshould follow at said intersection or junction; pre-informationdetecting means for detecting whether or not said pre-information hasbeen issued by said informing means; and means for inhibiting said guidemeans for providing guidance from issuing said guidance by said voicesound at said position immediately before said intersection or junctionwhen said pre-information detecting means detects that saidpre-information has not been issued.
 6. A navigation system for avehicle for guiding a vehicle along a route to a destination by issuingguidance with a voice sound at an intersection or junction, saidnavigation system comprising:map information storing means for storingmap information; computing means for computing said route to saiddestination by using said map information stored in said map informationstoring means; present position detecting means for detecting a presentposition of said vehicle; means for storing said route computed by saidcomputing means; and a route guiding control unit for providing outputmeans with one of pre-information voice guidance and final voiceguidance on a basis of said route stored in said means for storing saidroute and said present position of said vehicle detected by said presentposition detecting means, said route guiding control unitincluding:means for detecting whether or not said pre-information voiceguidance has been output by said route guiding control unit, and meansfor inhibiting output of said final voice guidance when said means fordetecting detects that said pre-information voice guidance has not beenoutput.
 7. A navigation system for a vehicle for guiding a vehicle alonga route co a destination by issuing guidance with a voice sound at anintersection or junction, said navigation system comprising:mapinformation storing means for storing map information; computing meansfor computing said route to said destination by using said mapinformation stored in said map information storing means; presentposition detecting means for detecting a present position of saidvehicle; means for detecting an accuracy in said detection of saidpresent position of said vehicle; means for storing said route computedby said computing means; and a route guiding control unit for providingoutput means with voice guidance to said destination on a basis of saidroute stored in said means for storing said route and said presentposition of said vehicle detected by said present position detectingmeans, said route guiding control unit inhibiting output of said voiceguidance when said accuracy in said detection of said present positionof said vehicle is below a predetermined value.
 8. A navigation systemaccording to claim 7, wherein said voice guidance relates informationregarding a direction said vehicle should follow at said intersection orjunction.
 9. A navigating system according to claim 7, wherein saidroute guiding control unit is further for:providing pre-informationvoice guidance when said vehicle reaches a predetermined distance shortof said intersection or junction; issuing a final voice guidance whensaid vehicle is at a position immediately before said intersection orjunction; and inhibiting output of said final voice guidance when saidaccuracy of said detected present position of said vehicle is less thansaid predetermined value.
 10. A navigating system according to claim 7,wherein said route guiding control unit is further for:inhibiting outputof said voice guidance when said accuracy of said detected presentposition of said vehicle is less than a first predetermined value;permitting output of said voice guidance when said detected accuracy isgreater than a second predetermined value which is greater than saidfirst predetermined value; and changing a content of said voice guidancewhen said detected accuracy is between said first predetermined valueand said second predetermined value.